I've been playing the Scheveningen for several months in CC, via the move order 2...e6 and 5...d6. This seems the most precise to me, since 3.Bb5+ is avoided and there is no corresponding cost. I predict that increasing attention will be payed to the Scheveningen, since the dread Keres Attack appears to have been mostly defanged. Personally I think it's a notable advantage not to have expended a move on ...a6, and the Scheveningen reached directly also avoids a number of dangerous antiNajdorf systems such as 6.Bg5.
In one of my first attempts with this defense, I lost after 1.e4 c5 2.Nf3 e6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 d6 6.g4 h6 7.h4 Nc6 8.Rg1 h5 9.gxh5 Nxh5 10.Bg5 Nf6 11.Be2 a6 12.Qd2 Qb6 13.Nb3 Bd7 14.h5 Nxh5 15.Rh1 g6 16.OOO Qxf2 17.e5. At this point I made the mistake of following Pritchett, playing his recommended 17...Qf5? 18.exd6! Qxg5 (what else?) 19.Qxg5 Bh6 20.Qxh6 Rxh6 21.Na4! and Black really has no defense to the incursion of White's pieces on the queenside, not that I could find anyway.
Unfortunately, I decided not to follow the 2001 CC game SashinPopov, which continued instead 17...Nxe5! 18.Ne4! Qf5 19.Rh4! (19.Qe3 is considered inadequate for White in the 2nd edition of Experts, p.169, second column under heading "b") 19...Bc6 20.Nxd6+ Bxd6 21.Nd4 Nd3+ 22.Bxd3 Qe5 23.Nxe6! Here Popov played 23...Qe6? and lost. However, Black has 23...fxe6! 24.Bxg6+ (the inclusion of the moves 25.Re1 Qg3 doesn't appear to change anything) 24...Kd7 25.Bxh5 Bd5 and I defy anyone to demonstrate White's advantage. For example:
(a) 26.Bf4 Qf6 27.Bg5 Qe5.
(b) 26.c4 Rc8 27.Kb1 Rxh5 28.Rxh5 Rxc4 and although Black has only one pawn for the exchange, he has no chance of losing that I can see.
(c) 26.Kb1 Rac8 or 26...Rag8.
Another significant challenge to the Scheveningen is what Pritchett calls the "Suetin Attack," 1.e4 c5 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 e6 6.f4 Nc6 7.Be3 Be7 8.Qd1f3 e5 9.Nd4xc6 bxc6 10.f5.
Pritchett recommends 10...Qa5, citing his game with Psakhis: 11.OOO Rb8 12.Bc4 h5 13.Bb3 Ba6 14.h3 h4 15.g4 hxg3 16.Qxg3 Rh7 17.h4 c5. Here Psakhis played 18.Bg5 and drew. But much stronger 18.h5!, after which Pritchett gives 18...c4 19.Ba4+ Kf8 20.h6 Qb4 21.hxg7+ Kb8 22.Rxh7 Qxb2+ as equal. This overlooks both 22.Bb3! and 22.Bb5!, each of which wins brilliantly for White. After 19.Ba4+ Black has to play 19...Kd8, but it's difficult to believe in Black's game then; e.g. 20.a3. So Black has some work to do in Pritchett's main line.
A critical alternative for Black is 10...OO 11.OOO Qd8a5 12.Bf1c4 (12.g4 d5 13.exd5 Be7b4 14.g5 e4 15.Qf3f4 Nf6xd5 16.Nc3xd5 cxd5 17.Qf4e5 Qa5xa2 18.c3 Bc8xf5 19.Be3d4 f6 20.gxf6 Bf5g4 21.Rd1e1 1/21/2 is a corr game of mine) 12...Ra8b8 13.Bc4b3 d5 14.exd5 Rb8xb3 15.cxb3 cxd5 16.Rd1xd5 Nf6xd5 17.Nc3xd5 Be7d6 18.Rh1d1 Qa5xa2 19.Nd5f6 Kg8h8 20.Rd1xd6 gxf6 21.Be3d2 Qa1+ 22.Kc2 Qg1 23.Rxf6 Qc5+ as played in Kunzelmann  Turicnik, corr 2007. Actually I have a corr game in progress from this position. I am not entire sure that Black has enough to draw. Turicnik managed to draw after 24.Kb1, but White also has 24.Bc3, which appears to me to be stronger.
So I'm not sure that the Suetin Attack is so easy for White to meet. It's worth noting though that if White tries to reach this via 1.e4 c5 2.Ng1f3 e6 3.d4 cxd4 4.Nf3xd4 Ng8f6 5.Nb1c3 d6 6.Bc1e3 Bf8e7 7.f4, Black has 7...OO 8.Qd1f3 e5! 9.Nd4f5 Bc8xf5 10.exf5 Nb8d7 11.OOO Qd8a5 with powerful counterplay. I have an ongoing corr game with 12.g4 Ra8c8 13.g5 Rc8xc3 14.gxf6 Nd7xf6 15.bxc3 d5 16.fxe5 Qa5xc3 17.Rd1d4 Qc3e1 18.Kc1b2 Be7a3 19.Kb2b3 Qe1a1 20.Kb3xa3 Qa1c3 21.Ka3a4 a6 22.Rd4xd5 Rf8a8 23.exf6 b5 24.Bf1xb5 axb5 25.Ka4xb5 Ra8b8 26.Be3b6 Qc3xf3 27.Rh1d1 Qf3e2 28.Kb5a5 gxf6 29.Rd5d8 Rb8xd8 30.Rd1xd8 Kg8g7 31.a4 Qe2xc2 32.h4 Qc2xf5 33.Ka5a6 Qf5f1 34.Ka6a7 f5 35.a5, an interesting position where I believe that Black is the only one with chances to win.
Once again, I will come back and edit this to add some more about the Scheveningen, but I post now so as not to lose what I've already written.
